A biotyping system for Staphylococcus aureus strains is proposed which is a simplified version of biotyping procedures described in the literature. It differentiates Staph. aureus strains from man and animals into host-specific ecovars and biotypes which are not host-specific. With the help of tests for beta-haemolysin, staphylokinase , coagulation of bovine plasma and the crystal-violet reaction, the origin of many but not all Staph. aureus strains can be determined: 604 of 809 strains from man, poultry, cattle, pigs, goats, rabbits and foods could be alloted to four ecovars which are typically associated with man, poultry, sheep and goats and cattle. The other strains belonged to five non-host specific biotypes.